This invention relates generally to gas generant chemical synthesis and, more particularly, to the synthesis of hexammine cobaltic salts such as for use in various gas generation applications and, in particular, for use in or in connection with vehicular occupant inflatable safety restraint systems.
Gas generating materials are useful in a variety of different contexts. One significant use for such compositions is in the operation of safety restraint systems adapted for providing protection to vehicle occupants. One common form of such a restraint system relies on one or more automotive inflatable restraint airbag cushions. It is well known to protect a vehicle occupant using a cushion or bag, e.g., an “airbag cushion,” that is inflated or expanded with gas when the vehicle encounters sudden deceleration, such as in the event of a collision. In such systems, the airbag cushion is normally housed in an uninflated and folded condition to minimize space requirements. Such systems typically include one or more crash sensors mounted on or to the frame or body of the vehicle to detect sudden decelerations of the vehicle and to electronically trigger activation of the system. Upon actuation of the system, the cushion begins to be inflated in a matter of no more than a few milliseconds with gas produced or supplied by a device commonly referred to as an “inflator.” In practice, such an airbag cushion is desirably deployed into a location within the vehicle between the occupant and parts of the vehicle interior, such as a door, steering wheel, instrument panel or the like, to prevent or avoid the occupant from forcibly striking such parts of the vehicle interior.
Gas generant compositions commonly utilized in the inflation of automotive inflatable restraint airbag cushions have previously most typically employed or been based on sodium azide. Such sodium azide-based compositions, upon initiation, normally produce or form nitrogen gas. While the use of sodium azide and certain other azide-based gas generant materials generally meets current industry specifications, guidelines and standards, such use may involve or raise potential concerns such as relating to the safe and effective handling, supply and disposal of such gas generant materials.
In view of such concerns, significant efforts have been directed to minimizing or avoiding the use of sodium azide in automotive airbag inflators. Hexammine cobaltic salts, such as in chloride, bromide, perchlorate, or nitrate form, constitute a family or class of materials that has drawn interest as or as a part of gas generating compositions for such gas generation applications. In particular, hexammine cobalt nitrate, i.e., Co(NH3)6(NO3)3, (also know as “HACN”), has drawn significant interest in view of various desirable features or characteristics. For example, the combustion or gas-generating reaction of HACN or of a HACN-based formulation to generate or produce substantial quantities of inflation gases, such as N2, can be accomplished almost instantaneously by initiating the gas generation reaction via the simple application of heat or through the use of a suitable igniter device such as of conventional design. Further, HACN provides a relatively high gas output (such as measured on a moles per 100 grams basis). For example, whereas sodium azide has a gas output of approximately 1.50 moles per 100 grams, HACN and HACN/carbon mixtures commonly have gas outputs in excess of 3.50 moles per 100 grams, with such materials typically having gas outputs in the range of about 3.89 to about 3.96 moles per 100 grams. Still further, HACN is a near monopropellant and thus can be practically employed in various gas generating applications without requiring substantial quantities of additional ingredients.
Greater commercial use of HACN, however, has generally been limited or restricted due to a general lack of availability of a suitable method for synthesizing HACN and HACN-based compositions in a manner which is either or both cost effective and time efficient as may be desired. For example, U.S. Pat. No. 5,972,304 is stated as directed to providing a process for producing HACN which saves energy by avoiding multiple alternating heating and cooling steps, which can be performed with a lesser amount of activated carbon and less expensive reagents, which reduces the amount of the potentially environmentally harmful waste, and in which the resultant HACN product is directly obtainable, in a high yield, in particles of acceptable size and purity for use in gas generant compositions. This patent discloses a process wherein an ammonium source, such as ammonium hydroxide, is added to a reaction solution containing at least one cobalt(II) salt having the molecular formula CoX2 and at least one ammonium salt of X where X is, by preference, a selected inorganic anion. The patent further discloses that the reaction solution is aged a predetermined period of time dependent on the aging temperature, wherein the aging temperature is preferably in the range of about 20° C. to about 35° C., and more preferably about 26° C. to about 32° C., and the required aging processing time is at least about 24 hours. As will be appreciated by those skilled in the art, however, processes which involve such extended processing times are generally not conducive to use in large scale manufacturing applications. Further, such processing has generally failed to result in HACN product of consistent and desired performance qualities.
In view thereof, there is a need and a demand for a method or manner of making a hexammine cobaltic salt, such as HACN, which is either or both more cost effective and time efficient as compared to commonly known or currently available methods of making such materials. Further, there is a need and a demand for a manner of making a hexammine cobaltic salt, such as HACN, which desirably results in a hexammine cobaltic salt product of consistent and desired performance qualities.